1. Field of the Invention
The invention relates generally to the field of oilfield isolation elements. Specifically, the invention relates to degradable isolation elements.
2. Background Art
It is common to use isolation elements, such as plugs or darts, to temporarily block fluid flow in tubular equipment. The tubular equipment may include oilfield tubular equipment, and tubular equipment used in geothermal wells, injection wells, and carbon dioxide sequestration wells. Isolation elements are used so that fluid pressure and flow may be applied to a specific portion of a well, without damaging or effecting downstream equipment. FIG. 1 shows a schematic of a well where such a device may be useful.
FIG. 1 shows a well 1 with a tubular 2 placed in the well 1. A casing 3 lines an upper portion of the well 1. Below the casing shoe 4, completion equipment is installed in the open hole. The equipment is designed to isolate two zones in the formation 5, an upper zone 11 and a lower zone 12. The upper zone 11 is bounded by an upper packer 6 and a lower packer 8, and the lower zone is bounded by an upper packer 10. It is noted that the lower zone 12 may also be bounded by a lower packer, although one is not shown in FIG. 1. It is also noted that wells may include more or less than two zones, as is known in the art.
In one example, it may be desirable to perform an operation on the upper zone 11, such as a gravel pack or a hydraulic fracture, without effecting the lower zone 12. The zones 11, 12 are isolated by the packers 6, 8, 10, which prevent fluid communication in the annulus outside the tubular string 2. Before the operation may begin, however, fluid communication between the two zones 11, 12 within the tubular string 2 must be prevented.
To accomplish this, a dart or plug, known in the art, may be dropped, lowered on a tool, or otherwise released into the tubular string 2 so that is seats in the seat 15. Once the dart is seated in the seat 15, fluid flow and pressure may be applied above the seat 15, and the dart will prevent fluid communication below the seat 15. A fracture or gravel pack operation may be performed on the upper zone 11, without effecting the lower zone 12 or the equipment below the seat 15.
Once the operation is performed, the dart (not shown) must be removed so that fluid communication within the tubular string 2 is reestablished.